1. Field of the Invention
The present invention relates generally to integrated circuit devices, and more specifically to variable impedance power supply delay elements for use in such integrated circuit devices.
2. Description of the Prior Art
Throughout the design, test, and manufacture of integrated circuit devices, such as memory devices, there exists the need to determine circuit performance. Especially during circuit debug, speed optimization, and yield optimization, certain device parameters and corresponding critical signals must be evaluated. Such critical signals may include sense amp timing, set-up and hold times, rise and falls times, etc. Evaluation of critical signals is often accomplished by introducing delays to the critical signals to change the timing of these critical signals and then measuring how the circuit responds to such delays.
Introduction of delays is often controlled by delay elements. It is often necessary to distribute delay elements throughout the integrated circuit in order to effect a global delay for a critical signal, since the critical signal may be distributed across a chip or within repeated circuit blocks. For example, sense amp timing delays are often times found in each memory block. It is common for sense amp timing delays to be introduced to 8, 16, 32, or more circuit blocks.
There are several methods currently used in the art to introduce delays in critical signal timing. Adjustments in the delay of critical signals may be accomplished using experimental masks, but this is costly and time consuming. It could be done using a focused ion beam (FIB), but when a number of circuit blocks must be adjusted, this can be quite time consuming, prone to error, and expensive. FIB is best suited for adjusting the circuitry at a limited number of locations, rather than repetitive operations. Also, FIB does not allow for production adjustment by blowing fuses and is therefore not ideal for a production environment. Additionally, placing fuses in each delay circuit takes a great deal of layout area and is cumbersome to layout in the central block control area of the chip.
To date, methods for introducing delays to critical integrated circuit signals have required the placement of delay elements throughout the integrated circuit in distributed circuit blocks. The distribution of delay elements throughout the integrated circuit means that adjustments to these delay elements must be made at multiple locations. Methods currently used to do this, as described above, may be time consuming, prone to error, expensive, and not desirable for a production device.